Wireless communication systems have been in wide use as a data communication means because of such convenience that communication terminals used by users are portable and thus the places to use them are not restricted. Mobile communication terminals are powered by a battery, so that a power saving capability is required.
As one example of a wireless communication system, there is a wireless LAN system specified by IEEE 802.11. In the wireless LAN system, an infrastructure mode and an ad-hoc mode are provided so as to perform communication with another wireless communication apparatus. The ad-hoc mode refers to a mode in which wireless LAN terminals directly transmit and receive data. Meanwhile, the infrastructure mode refers to a mode in which a plurality of wireless LAN terminals are connected to a wireless communication apparatus called an access point, and the wireless LAN terminals performs data transmission and reception via the access point.
The wireless LAN system conforming to the IEEE 802.11 scheme specifies a specification related to a power saving mode for controlling power consumption (for example, see Non Patent Literature 1). Further, it is known that the wireless LAN terminal has two types of modes: an awake mode capable of receiving data; and a doze mode which operates in a low power without transmission and reception.
Here, when the access point receives data addressed to a wireless LAN terminal associated with an own apparatus, the access point once stores the data in a communication buffer. The access point transfers the data when the wireless LAN terminal which is the destination of the data is operating in the awake mode. Meanwhile, when the wireless LAN terminal is operating in the doze mode, the access point transmits a beacon including an element called a traffic indication map (TIM). Specifically, the access point sets a corresponding bit to a TIM indicating that data addressed to a corresponding wireless LAN terminal is buffered, and transmits a beacon including the TIM.
The wireless LAN terminal operating in the power saving mode transitions to the doze mode according to an interval of a beacon frame periodically transmitted by the access point. The wireless LAN terminal that has transitioned to the doze mode receives the beacon including the TIM indicating that there is data addressed to the wireless LAN terminal. The wireless LAN terminal that has received the beacon including the TIM transmits a data delivery request to the access point, notifies the access point of the fact that it has transitioned to the awake mode, and then receives the data. The wireless LAN terminal in the awake mode transitions to the doze mode again when there is no data addressed to the wireless LAN terminal.
Meanwhile, when there is a plurality of wireless LAN terminals associated with to the access point, the access point notifies of the fact that there is buffer data addressed to the plurality of wireless LAN terminal by the TIM. Due to the notice to the plurality of wireless LAN terminals, data delivery requests from the wireless LAN terminals operating in the doze mode are concentrated, and the number of wireless LAN terminals operating in the awake mode to acquire a transmission right increases. For this reason, there is a problem in that the power consumption of these wireless LAN terminals increases.
In this regard, in order to solve the above problem, for example, Patent Literature 1 discloses a technique of allowing wireless LAN terminals to independently set a beacon acquisition period and preventing data delivery requests from wireless LAN terminals from being concentrated at a certain timing.
Further, Patent Literature 2 discloses a technique of notifying of the presence of buffer data only when a determination criterion according to a data type is satisfied when an access point receives data addressed to a subordinate wireless LAN terminal.